In these years, there has been an increase in the cases of using display devices in environments with a lot of dust particles such as in stores and the outdoors, for example. In the case where dust particles enter the inside of the projection display device, the dust particles become attached to optical components to cause phenomena including a reduction in brightness, color irregularities, or the reflection of the attached dust particles in projection images, resulting in a reduction in optical performance. For this reason, the techniques of improving dust-proof properties of the projection display device are important. For dustproof structures relating to the present invention, such configurations are disclosed in which the projection display device is entirely dust-proofed and an LCD unit is dust-proofed.
In JP2003-241310A (Patent Document 1), a configuration is disclosed in which a projection display device is entirely covered with a protection cabinet and the protection cabinet is provided with an air filter and cooling fans. In this dustproof structure, dust particles are removed from air admitted from the outside into the inside of the protection cabinet with the air filter, so that the entire projection display device is surrounded by cooling air after dust particles are removed.
In addition, JP2007-292805A (Patent Document 2) describes a projection display device that is a so-called three-plate liquid crystal projector in which an LCD panel (in the following, abbreviated to LCD) that generates images to be projected is individually provided in a red optical path (R optical path), green optical path (G optical path), and blue optical path (B optical path). In addition, in this description, “red” is abbreviated to R, “green” to G, and “blue” to B. In Patent Document 2, a configuration is disclosed in which dust particles are removed from cooling air supplied to an LCD unit having three LCDs. On the discharge side of a cooling fan that delivers cooling air to the LCD unit, draft air ducts are provided, each of which corresponds to the G optical path and the B optical path, and different air filters are individually provided for these draft air ducts. To the G optical path and the B optical path, cooling air is delivered, from which dust particles are removed with the air filters.
In this dustproof structure, generally, the B component in optical energy applied to the LCD is the largest and the R and G components are almost the same, so that a configuration is adopted in which priority for cooling is accorded to B optical path ahead of G optical path. Thus, in this dustproof structure, the dust collection performance of the air filter provided in the draft air duct for the B optical path is set lower than that of the air filter provided in the draft air duct for the G optical path. With this configuration, the draft air duct for the B optical path has ventilation resistance, which is caused by the air filter, smaller than that of the draft air duct for the G optical path, resulting in an improved cooling performance.
Now, the configuration described in Patent Document 1 mentioned above is the configuration in which the entire projection display device is dust-proofed by removing dust particles that are contained in the entire cooling air admitted into the projection display device. Because of this, this configuration has a poor cooling performance of the projection display device, resulting in a relatively large calorific value of the projection display device. Consequently, in this configuration, a large air quantity is necessary to sufficiently cool the entire projection display device. On one hand, in order to improve dust-proof properties, it is necessary to use an air filter with a relatively smaller filter mesh size, so that the air filter tends to be clogged. More specifically, in this configuration, an air filter having a relatively large area is needed such as an air filter equipped in an air cleaner, for example. Moreover, because of the configuration in which the entire projection display device is covered with the protection cabinet, the size and weight of the device is increased, and it is necessary that the protection cabinet have a structure that maintains high sealing properties. Furthermore, for the cooling fan equipped in the projection display device, it is necessary to provide a plurality of high static pressure fans in order to overcome the ventilation resistance of the air filter.
However, even in the case of using the air filter with a relatively large area, the air filter is sometimes clogged due to the use of the air filter in adverse environments or due to its use for a long period of time. In the case where the air filter is clogged, it becomes difficult to deliver sufficient cooling air to components mounted on the inside of the projection display device. As a result, the temperature of the mounted components increases which causes malfunctions, resulting in a considerably shortened lifetime of the mounted components. In addition, the projection display device may even be stopped because of the activation of a protection circuit.
Moreover, in the configuration described in Patent Document 2 mentioned above, because the air filters are provided in the draft air ducts, whose opening area is relatively narrow, on the discharge side of the cooling fan, it is difficult to sufficiently and without fail provide the cross sectional area for ventilation, and the air filters tend to be clogged. Because the dust collection performance of the air filter provided in the draft air duct for the B optical path is poor, clogging tends to occur in the air filter provided in the draft air duct for the G optical path. In the case where the air filter provided in the draft air duct for the G optical path is clogged, the air quantity increases in the draft air duct for the B optical path with a small ventilation resistance. Thus, the temperature of the optical components provided in the draft air duct for the G optical path rapidly rises. The increase in the air quantity in the draft air duct for the B optical path causes clogging also in the air filter in the draft air duct for the B optical path, resulting in a considerable increase in the temperature of the optical components due to inevitable blockage of the draft air ducts in both optical paths. Thus, a reduction in the lifetime of the mounted components and breakage of the mounted components tend to occur.
Furthermore, in the configuration described in Patent Document 1, the dust collection performance of the air filter provided in the B optical path is lower than that of the air filter provided in the G optical path. Because of this, this configuration has problems in which a reduction in brightness is greater in the B optical path than in the G optical path and in which projection images are tinted yellow, that is, the temperature rises.
Moreover, in the configuration described in Patent Document 1, the air filter is provided in the draft air duct on the discharge side of the cooling fan, and this causes the ventilation area of the draft air duct to become narrow, resulting in a large increase in ventilation resistance. Consequently, in order to implement the desired cooling performance, it is necessary to increase the number of revolutions of the cooling fan, causing a problem in which noise is increased with the rotation of the cooling fan. More specifically, the configuration of this dustproof structure has problems in which the air filter tends to be clogged, projection images are tinted yellow, and noise is increased.
Furthermore, it is necessary for the projection display device, which is installed in adverse environments having a considerable amount of dust particles, to frequently change the air filter. However, in the configurations of the aforementioned two publications an operation is required for disassembling the projection display device when removing the air filter, thus causing a problem in which changing the air filter becomes a complicated operation. Consequently, in consideration of frequent change of the air filter, the aforementioned configurations cannot sufficiently be adapted to the projection display device installed in adverse environments.